It is well known in the roofing industry that irregularity or variation in shingle design provides a roof that is esthetically pleasing and in popular demand. Mass produced asphalt roofing shingles of the ordinary three-tab variety, when placed on the roof, result in a roof which sometimes appears flat, dimensionless and uninteresting. Shingle manufacturers have attempted to provide a better look to such roofs by using variations in the thickness and in the tab cutout design of shingles. The goal is to produce a random looking sequence or pattern of shingles on the roof, similar to the appearance given by a roof shingled with wood shingles having varying widths, lengths and thicknesses.
Innovations to improve the random-like character of shingles include the use of a laminated shingle, which consists of an overlay having tabs and cutouts, and an underlay, which is usually rectangular. These laminated shingles can be produced in an offline system whereby the overlays are formed and cut and later mated with an already cut underlay for lamination. Another method of making laminated shingles involves an inline system in which continuous overlay and underlay strips are laminated together and then the laminated continuous strips are cut with an endcut cylinder into individual shingles.
Typical shingle manufacturing techniques include the use of a cutting cylinder positioned to engage the continuous shingle membrane and cut the design of the shingle. For a typical three-tab shingle, the cutting cylinder has a circumference the same length as the length of the shingle. This length is typically either 36 inches or 393/8 inches. In the case of a laminated shingle, where the cutting process and the lamination process occur prior to the end cutting process, the cutting cylinder does not divide the continuous shingle membrane into discrete roofing shingles. The laminated continuous membrane strips are cut into discrete roofing shingles by the endcut cylinder, positioned downstream from the cutting cylinder. The length of the shingle will always be the circumference of the endcut cylinder.
Where the cutting cylinder has a circumference equal to the length of the shingle, the relationship between the cutting cylinder and the length of the shingle is called a one-around system. Another system which may have been employed in the art is a two-around system, which uses a cutting cylinder with a circumference equal to twice the length of the shingles. With the two-around cutting cylinder, the cylinder cutting pattern can produce two distinct shingles with each revolution. In both the one-around and the two-around systems, the circumference of the cutting cylinder and the length of the shingle have a common factor--the length of the shingle. The one-around and two-around systems are limited in that there are at most only four different shingles produced: the two patterns around the circumference and their complements.
The third type of sequencing between the cutting cylinder and the endcut mechanism is the near random type relationship, where the endcut cylinder does the end cutting, but the cutting cylinder circumference is not equal to, or a multiple of, the shingle length.
In this system the length of the shingle differs from the circumference of the cutting cylinder. The shingles will then be cut always in a different place, thereby creating a multitude of shingle patterns, approaching a random shingle pattern, but repeating after a large number of revolutions. For example, if the cutting cylinder is 40 inches in circumference, and the endcut cylinder (and the length of the shingle) is 39 inches, then the shingle pattern will repeat itself after producing approximately 39 shingles.
The fourth type of sequencing between the cutting cylinder and the endcut mechanism is the random relationship. In such a case, there is no specific relationship between the length of the shingle and the circumference of the cutting cylinder. In the random cutting system the shingles are endcut downstream from the cutting cylinder, and the endcut cylinder is not maintained in phase with the shingle pattern. The shingles will then be cut in different places, thereby creating truly random shingle patterns.
The random and near-random endcut practice produces some undesirable characteristics. First, the use of a random or near-random cut does not always produce a random looking roof when the shingles are applied. Second, the use of a random or near-random cut with a laminated shingle having tabs and cutouts, can result in shingle tabs that are relatively narrow, such as being narrower in width than about 1.4 inches. It has been found that handling the shingle during the manufacturing process and during the installation process on the roof, where tabs are narrower than about 1.4 inches, can result in a tearing away of the tabs. This causes a maintenance problem in the plant and during installation, and alters the appearance of the shingle on the roof. It would be desirable to have a shingle-cutting pattern and system whereby shingle tabs are not made more narrow than about 1.4 inches in order to prevent the breaking off of the narrow shingle tabs.